64 



STRUCTURAL BOTANY. 



first pair of leaves. But sometimes when they are very thick, as 

 in Pea, Buckeye, and Oak, they never escape the seed-coats, but 

 remain and perish at the collum ( 199), neither ascending nor 

 descending. 



225 



Germination of the Maple. -225, Samara; section showing the folded cotyledons at c. 226-230, Pro- 

 gressive stages. 



193. The germination of MONOCOTYLEDONS, as seen in Indian 

 Corn, Wheat, and Tulip, is in this wise. The cotyledon is not 

 disengaged from the seed, but remains stationary with it. The 

 radicle (r) protrudes slightly, and one or more rootlets (s) break 

 out from it and descend. The plumule (c) shoots at first par- 

 allel with the cotyledon along the face of the seed, but soon 

 ascends, pushing out leaf from within leaf. 



194. The conditions requisite for germination are moisture, 

 air, and warmth. Moisture is necessary for softening the integ- 

 uments, dissolving the nutritive matter, and facilitating its cir- 

 culation. This is supplied in the rain and dew. Air, or rather 

 its oxygen, is required for the conversion of the starch into 

 sugar, a process always depending upon oxidation. The oxy- 

 gen absorbed unites with a portion of the carbon of the starch, 

 producing heat, evolving carbonic acid, and thus converting the 

 remainder into grape-sugar, soluble and nutritive. 



195. Warmth is a requisite condition of all vital action, as 



